- * When a shared resource becomes available the {@link #signal()} method should - * be called unconditionally. - *
- * A thread wishing to acquire a shared resource should:
- *
true result from {@link #waitUntilSequenceExceeded(long, long)},
- * the current sequence should again be obtained from the {@link #currentSequence()} method,
- * and an attempt to acquire the resource should be made. false is received from {@link #waitUntilSequenceExceeded(long, long)}
- * then a timeout has occurred. - * When running on Java 8 and above, this class leverages the fact that when {@link LongAdder} - * is monotonically increasing, and only {@link LongAdder#increment()} and {@link LongAdder#sum()} - * are used, it can be relied on to be Sequentially Consistent. - * - * @see Java Spec - * @author Brett Wooldridge - */ -public final class QueuedSequenceSynchronizer -{ - private final Sequence sequence; - private final Synchronizer synchronizer; - - /** - * Default constructor - */ - public QueuedSequenceSynchronizer() - { - this.synchronizer = new Synchronizer(); - this.sequence = Sequence.Factory.create(); - } - - /** - * Signal any waiting threads. - */ - public void signal() - { - synchronizer.releaseShared(1); - } - - /** - * Get the current sequence. - * - * @return the current sequence - */ - public long currentSequence() - { - return sequence.get(); - } - - /** - * Block the current thread until the current sequence exceeds the specified threshold, or - * until the specified timeout is reached. - * - * @param sequence the threshold the sequence must reach before this thread becomes unblocked - * @param nanosTimeout a nanosecond timeout specifying the maximum time to wait - * @return true if the threshold was reached, false if the wait timed out - * @throws InterruptedException if the thread is interrupted while waiting - */ - public boolean waitUntilSequenceExceeded(long sequence, long nanosTimeout) throws InterruptedException - { - return synchronizer.tryAcquireSharedNanos(sequence, nanosTimeout); - } - - /** - * Queries whether any threads are waiting to for the sequence to reach a particular threshold. - * - * @return true if there may be other threads waiting for a sequence threshold to be reached - */ - public boolean hasQueuedThreads() - { - return synchronizer.hasQueuedThreads(); - } - - /** - * Returns an estimate of the number of threads waiting for a sequence threshold to be reached. The - * value is only an estimate because the number of threads may change dynamically while this method - * traverses internal data structures. This method is designed for use in monitoring system state, - * not for synchronization control. - * - * @return the estimated number of threads waiting for a sequence threshold to be reached - */ - public int getQueueLength() - { - return synchronizer.getQueueLength(); - } - - private final class Synchronizer extends AbstractQueuedLongSynchronizer - { - private static final long serialVersionUID = 104753538004341218L; - - /** {@inheritDoc} */ - @Override - protected long tryAcquireShared(final long seq) - { - return sequence.get() - (seq + 1); - } - - /** {@inheritDoc} */ - @Override - protected boolean tryReleaseShared(final long unused) - { - sequence.increment(); - return true; - } - } -} diff --git a/src/main/java/com/zaxxer/hikari/util/Sequence.java b/src/main/java/com/zaxxer/hikari/util/Sequence.java deleted file mode 100644 index b7abd3ce..00000000 --- a/src/main/java/com/zaxxer/hikari/util/Sequence.java +++ /dev/null @@ -1,71 +0,0 @@ -/* - * Copyright (C) 2015 Brett Wooldridge - * - * Licensed under the Apache License, Version 2.0 (the "License"); - * you may not use this file except in compliance with the License. - * You may obtain a copy of the License at - * - * http://www.apache.org/licenses/LICENSE-2.0 - * - * Unless required by applicable law or agreed to in writing, software - * distributed under the License is distributed on an "AS IS" BASIS, - * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - * See the License for the specific language governing permissions and - * limitations under the License. - */ - -package com.zaxxer.hikari.util; - -import java.util.concurrent.atomic.AtomicLong; -import java.util.concurrent.atomic.LongAdder; - -/** - * A monotonically increasing long sequence. - * - * @author brettw - */ -@SuppressWarnings("serial") -public interface Sequence -{ - /** - * Increments the current sequence by one. - */ - void increment(); - - /** - * Get the current sequence. - * - * @return the current sequence. - */ - long get(); - - /** - * Factory class used to create a platform-specific ClockSource. - */ - final class Factory - { - public static Sequence create() - { - if (!Boolean.getBoolean("com.zaxxer.hikari.useAtomicLongSequence")) { - return new Java8Sequence(); - } - else { - return new Java7Sequence(); - } - } - } - - final class Java7Sequence extends AtomicLong implements Sequence { - @Override - public void increment() { - this.incrementAndGet(); - } - } - - final class Java8Sequence extends LongAdder implements Sequence { - @Override - public long get() { - return this.sum(); - } - } -}